Sacrificial liners are secured to the internal casing of ore mills. They are typically provided as segments, and they are secured internally of the mill shell by bolts which are fitted from the internal side of the shell and project through apertures in the liners and through mounting bores in the shell. A nut and sealing washer are threaded onto and tightened onto each bolt from outside the shell, drawing the liner to the inner surface of the shell. An example of a conventional liner segment fastener system is shown in US Pat. No. 4,018,393 (Larsen). Typically the bolts used for such application are referred to as linerbolts.
Ore mills are generally run continuously for economic efficiency. The continuous process wears down the liners over a period of time, which will depend on the type of ore and application, after which the liners will have to be replaced. Because down time of the ore mill adversely affects the economic efficiency of the process, it is essential to change liners as quickly as possible.
In such applications, the bolts on liners become corroded and clearances between bolts and holes become compacted with ore fines. This results in difficult bolt removal. As a result the many bolts that are utilised to attach the liners to the mill shell are often required to be freed manually by the use of large sledge-hammers, and more frequently by percussive devices such as jack-hammers and hydraulically powered hammers to provide repetitive impacts.
Liner replacement involves removal of nuts, typically followed by hammering the exposed bolt from the outside the mill. In known hammering devices capable of delivering the necessary impacts, a high reaction force is produced which necessitates that such devices be carried by articulating machines or be rigidly attached to some support structure. Various types of hydraulic and pneumatic hammering devices, commonly referred as linerbolt removal tools, are shown in International publication W097/26116 (Russell Mineral Equipment Pty Ltd), US Pat. No. 6,904,980 (Rubie) and US Pat. No. 8,196,676. (Rubie).
Typically linerbolt removal tools are suspended from monorails or telescoping jibs, which requires manual manipulation and leads to error in tool alignment. Whilst efficiency has improved over the years with use of linerbolt removal tools, it is desirable to further improve the replacement of liners.
US Patent Publication No. 2007/0180678 (Salamanca) and US Patent Publication No. 2012/0102703 (Salamanca) propose a robotized method of removing bolts from SAG and/or ball mills. A five-axis anthropomorphic robot mounted on rails is used to address handling and alignment issues. However, such an anthropomorphic robot is an expensive option particularly when two or more robots are disposed around the mill. Furthermore such robot requires a complicated control system.
The present invention seeks to overcome at least some of the abovementioned disadvantages by providing an improved apparatus for suspending and guiding a tool externally of a grinding mill.